Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Creating a Better Source of 118 nm Light

Benjamin Saarel

Published Jan 1, 2018• 0 citations
OpenAlex

Abstract

The observed molecule signal in cold molecule experiments is limited by the molecule source and the efficiency of the detection method. The purpose of my thesis work was to improve the scientific apparatus physicists use to trap and detect cold molecules. The first part of my thesis focuses on improving a new cold molecule source known as a Nijmegen Pulsed Valve by optimizing the parameters used to run it. The valve worked best when operating at a voltage of 8-12V, valve pulse duration of 70-100 microseconds, and valve frequency of 1Hz. The new Neijmegen Pulsed Valve, run with optimized parameters, was then compared to the standard cold molecule source known as the Piezoelectric Valve. The two valves showed similar performance. The second part of my thesis focuses on investigating a method used to detect cold molecules, known as photoionization spectrometry with vacuum ultraviolet (VUV) light, with the overall goal of improving the method. A common VUV light source is 118 nm light produced by third harmonic generation (THG) in a mixture of xenon and argon. According to theory, it is possible to increase the amount of 118 nm light from THG by increasing the pressure of the phased matched Xe-Ar mixture, however the amount of 118 nm light decreases with increasing mixture pressure. One untested factor thought to be causing this discrepancy is linear absorption of 118 nm light in xenon. However, the tests I performed show that linear absorption in xenon is not the issue.

Related papers

Design and Characterization of a New Pulsed Molecular-Beam Valve

Ian W Collett

A common technique for producing samples of cold molecules that can be trapped and studied is electromagnetic deceleration of a fast moving, but internally cold, supersonic beam. The quality of these samples, which are ideally as cold and dense as possible, is fundamentally limited by the quality of the beam coupled to the decelerator. This thesis outlines the design, construction, and characterization of a new pulsed valve that produces samples of molecules as short as fifty microseconds.

•Jan 1, 2016•1 citation

Stark Deceleration Methods for Cold Molecule Experiments

Yomay Shyur

The growing field of cold molecule physics has demonstrated many methods of quantum control for precision measurement and molecular interaction studies. One particular method is Stark deceleration, which uses electric field gradients to produce packets of slow polar molecules. Since Stark deceleration does not increase phase-space density, the efficiency of the deceleration process is critical in determining the final cold molecule density. This dissertation describes three different Stark deceleration techniques. The first type of deceleration is pulsed-pin deceleration. We use this technique to produce slow OH molecules that can be trapped for cold collision studies. A two photon state-selective detection system, which includes a 118 nm photon, is used to determine the density distribution of OH in the trap. We explore the advantages and limitations to creating 118 nm light. The second and third types of Stark deceleration are pulsed-ring and traveling-wave methods of running a ring-geometry decelerator. Ring-geometry decelerators present improved deceleration efficiencies due to the cylindrical symmetry of the electrodes and true three-dimensional confinement. The pulsed-ring mode of the ring decelerator uses commercial high-voltage switches to apply discrete pulses to the ring electrodes. The continuous operation mode of the ring decelerator uses varying sine-wave voltages to create a traveling Stark potential well and has proven to be incredibly challenging due to the analog high voltage requirements of the system. In order to bring ND3 seeded in krypton (∼415 m/s) down to rest in the laboratory, sine wave voltages with amplitudes up to ±10 kV, currents up to 500 mA, and a bandwidth of 30 kHz down to DC are required. We describe a high-voltage amplifier that can be used for traveling-wave deceleration. The traveling-wave Stark deceleration mode is then compared to the pulsed-ring Stark deceleration mode and cases where one mode is superior to another are discussed.

•Jan 1, 2018•1 citation

Production, Deceleration, and Detection of OH Radicals

Travis Briles

Samples of cold and ultracold polar molecules have the potential to revolutionize physical chemistry, precision measurement, and few-body quantum physics. This thesis describes experimental results for the production of cold samples of OH radicals by Stark deceleration of a supersonic beam. Since Stark deceleration cannot increase the phase space density of the sample, the initial production stage of the OH molecule is critical. The first set of experiments describes a general methodology for the production of OH beams with maximal phase space density, as well as the subsequent coupling to a Stark decelerator. Additionally, we describe the redesign of our electrostatic trap, optimized for future collision experiments of OH with co-trapped ultracold Rb atoms. The new design resulted in a 15-fold increase in total number of trapped molecules over the previous design when tested with ND3 molecules. The second set of experiments focuses on laser-based detection of OH molecules at the exit of the decelerator based on laser induced fluorescence (LIF) and resonance enhanced multiphoton ionizaton (REMPI). The latter method uses vacuum-ultraviolet light at 118nm produced by third-harmonic generation in Xe/Ar gas mixtures as the ionizing step. The sensitivity of this latter technique is limited by the attainable photon flux of the ionizing radiation at 118nm. We present detailed measurements of the conversion efficiencies as well as absolute photon fluxes. Strategies to overcome these limitations as well as prospects for detection of OH molecules in a trap are discussed.

•Jan 1, 2015•0 citations

Towards hybrid trapping of cold molecules and cold molecular ions

Haas, Dominik

A pinhole discharge unit as well as a dielectric barrier discharge (DBD) head were developed for the Nijmegen pulsed valve (NPV) and the molecular beam properties accessible from each source were characterised and compared. The discharge conditions were optimised for maximum hydroxyl radical density. It was found that the DBD source yields colder OH radicals, whereas the pinhole discharge source provides a threefold larger radical density compared to the DBD discharge head. \n \nTranslationally cold packages of hydroxyl radicals (Ttrans > 1mK) were produced by means of Stark deceleration and a 124-stage Stark decelerator was set up in the laboratory. The decelerator was conditioned, characterised and optimised for operation at low final velocities (v < 40 m/s). The performance of the decelerator was assessed by determining the density of OH radicals available after the deceleration process. \n \nIn a final step, a translationally cold OH package was loaded into a cryogenic magnetic trap. The trap design, the coupling of the magnetic trap to the Stark decelerator and the loading efficiency were numerically optimised employing a direct search algorithm on Monte-Carlo trajectory simulations. The cryogenic environment efficiently prevents black-body radiation from pumping OH radicals out of trappable states and the background pressure improved significantly. Under cryogenic conditions the 1/e trap lifetime improved by a factor of 30 compared to room temperature. The magnetic trap forms part of a hybrid trapping scheme for neutral molecules and ionic species. This novel type of trap represents a versatile environment for investigating ion-neutral molecule reactions in the cold regime, while offering full control over the contributing quantum states.

•Jan 1, 2019•1 citation

A Source of Translationally Cold Molecular Beams

Laszlo C. Sarkozy

Currently the fields studying or using molecules with low kinetic energies are experiencing an unprecedented growth.Astronomers and chemists are interested in chemical reactions taking place at temperatures below or around 20 K, spectroscopists could make very precise measurements on slow molecules and molecular physicists could chart the potential energy surfaces more accurately.And the list continues.All of these experiments need slow molecules, with kinetic energies from around 10 cm -1 down to 0. Several designs of cold sources have already been made.The most interesting ones are presented.This work describes the design and the testing of a cold source based on the collisional cooling technique: the molecules of interest are cooled well below their freezing point by a precooled buffer gas.This way condensation is avoided.The source is a copper cell cooled to 4.2 K by an external liquid helium bath.The cell is filled with cold buffer gas (helium).The molecules of choice (ammonia) are injected through a narrow tube in the middle of the cell.The cold molecules leave the cell through a 1 millimeter hole.Two versions of pulsing techniques have been employed: a shutter blade which covers the source hole and opens it only for short moments, and a chopper that modulates the beam further downstream.Both produced pulse lengths around 1 millisecond.The source is tested in an experiment in which the emerging molecules are focused and detected.Time of flight technique is used to measure the kinetic energies.Two detectors have been employed: a microwave cavity to analyze the state of the molecules in the beam, and a mass spectrometer to measure the number density of the particles.The molecules coming out of the source hole are formed into a beam by an electrostatic quadrupole state selector.The quantum mechanical aspects and the elements of electrodynamics involved in the focusing are described.A computer simulation program is presented, which helped calculate the trajectories of the molecules from source to the final detector.The simulations revealed interesting artifacts the focuser can make: if a short state selector is used, the speed distribution of the beam arriving at the detector is strongly modulated by a "focuser transfer function".The essence of the phenomenon is caused by the inability of the focuser to focus all speed at the same time: a few velocity groups are well focused, while many others are defocused.The transfer functions gained from the simulations were used to correctly interpret the detector signal.iii The design of the microwave cavity (Fabry-Perot) and its driving electronics is presented.Due to unavoidable noises present in the circuit, the use of this detector was limited to the preliminary experiments.A simple, commercial mass spectrometer was used.To improve its characteristics, a few modifications have been made.With the improved version, only the water background (an interfering signal at mass 17 amu) was disturbing the signal.A liquid nitrogen trap has been used to minimize the background.The experimental measurements revealed several undesired effects accompanying the production of the slow beam: cluster formation, snow accumulation inside the cell and very high sensitivity to the balance of the two gas pressures.Clusters made up the majority of the emitted particles.Switching from the shutter-blade pulsing (closed cell) to the chopper modulation (open cell) improved the ratio of the useful molecules in the beam significantly.The snow accumulation limited the useful experimenting time to around 20 minutes.After this the accumulated ammonia snow either perturbed the signal significantly or obstructed the source hole completely.A very high sensitivity to the ratio of the buffer gas pressure to the ammonia injection rate has been noticed.A 30% deviation from the optimum value can change the speed distribution and the amount of emitted molecules completely.The stabilization of the ballast pressures was necessary.The beam obtained in the optimal regime of the source cell is presented and analyzed.The characteristic values of most interest in a future collision experiment are the following: the speed distribution of the beam at the detector has a height of the order of 10 5 molecules per unit speed interval and per pulse; the useful speed interval is from 55 m/s to 500 m/s.iv Dedicated to my wife, Magdi.v ACKNOWLEDGMENTS According to an East European folktale a king wanted to find out how much his daughters loved him.When the smallest princess answered "I love you like salt", the angry king banished her from the kingdom.It was only later, when the kingdom was totally deprived of salt, that he realized the real value of his daughter's words.I believe it was the salt of science that I received from my advisor, Frank De Lucia.His endless optimism always kept me going forward and taught me how to deal with difficulties now and in the future.He always made himself available, and never let me go without an excellent idea or a piece of advice.An exceptional scientist and a wonderful man, he will always be the distant example to follow in my scientific career.Gregory Lafyatis also deserves my gratitude for his insights into many of the theoretical aspects of my research.The instruments he lent me made my work in the lab much easier.I also thank Joe Demers for helping me in the lab at the most difficult time: the beginning.I am very thankful to my colleagues, Ivan Medvedev and David Graff for being always interested in my work and giving me valuable ideas.I am especially grateful to Christopher Neese for helping me with LabView related problems at a crucial moment of my research.I wish to thank Kent Ludwig for his tedious work on the low-temperature components of the experimental setup.Tom Kelch, advisor in the student mechanical shop, always had the right solution to the mechanical engineering problems I encountered.The team led by John Spaulding in the main mechanical shop did an excellent work, delivering countless pieces of exceptional quality in a

•Jan 1, 2008•0 citations

Tunable VUV light generation for the low-level resonant ionization detection of krypton

Steven D. Kramer, C. H. Chen, M. G. Payne +2 more

High-power tunable VUV light pulses with energies up to 0.7 μJ were generated in the 115.7–116.9-nm region by use of a two-photon resonant four-wave mixing scheme in a Xe–Ar gas mixture. This is the highest reported pulse energy that has been produced in this wavelength region using a four-wave mixing process. Efficient detection of krypton isotopes at densities as low as 10 atoms/cm3 was demonstrated by resonantly ionizing the atom through its one-photon allowed state at the vacuum wavelength of 116.49 nm.

Applied Optics•Oct 15, 1983•29 citations
The observed molecule signal in cold molecule experiments is limited by the molecule source and the efficiency of the detection method. The purpose of my thesis work was to improve the scientific apparatus physicists use to trap and detect cold molecules. The first part of my thesis focuses on improving a new cold molecule source known as a Nijmegen Pulsed Valve by optimizing the parameters used to run it. The valve worked best when operating at a voltage of 8-12V, valve pulse duration of 70-100 microseconds, and valve frequency of 1Hz. The new Neijmegen Pulsed Valve, run with optimized parameters, was then compared to the standard cold molecule source known as the Piezoelectric Valve. The two valves showed similar performance. The second part of my thesis focuses on investigating a method used to detect cold molecules, known as photoionization spectrometry with vacuum ultraviolet (VUV) light, with the overall goal of improving the method. A common VUV light source is 118 nm light produced by third harmonic generation (THG) in a mixture of xenon and argon. According to theory, it is possible to increase the amount of 118 nm light from THG by increasing the pressure of the phased matched Xe-Ar mixture, however the amount of 118 nm light decreases with increasing mixture pressure. One untested factor thought to be causing this discrepancy is linear absorption of 118 nm light in xenon. However, the tests I performed show that linear absorption in xenon is not the issue.
The growing field of cold molecule physics has demonstrated many methods of quantum control for precision measurement and molecular interaction studies. One particular method is Stark deceleration, which uses electric field gradients to produce packets of slow polar molecules. Since Stark deceleration does not increase phase-space density, the efficiency of the deceleration process is critical in determining the final cold molecule density. This dissertation describes three different Stark deceleration techniques. The first type of deceleration is pulsed-pin deceleration. We use this technique to produce slow OH molecules that can be trapped for cold collision studies. A two photon state-selective detection system, which includes a 118 nm photon, is used to determine the density distribution of OH in the trap. We explore the advantages and limitations to creating 118 nm light. The second and third types of Stark deceleration are pulsed-ring and traveling-wave methods of running a ring-geometry decelerator. Ring-geometry decelerators present improved deceleration efficiencies due to the cylindrical symmetry of the electrodes and true three-dimensional confinement. The pulsed-ring mode of the ring decelerator uses commercial high-voltage switches to apply discrete pulses to the ring electrodes. The continuous operation mode of the ring decelerator uses varying sine-wave voltages to create a traveling Stark potential well and has proven to be incredibly challenging due to the analog high voltage requirements of the system. In order to bring ND3 seeded in krypton (∼415 m/s) down to rest in the laboratory, sine wave voltages with amplitudes up to ±10 kV, currents up to 500 mA, and a bandwidth of 30 kHz down to DC are required. We describe a high-voltage amplifier that can be used for traveling-wave deceleration. The traveling-wave Stark deceleration mode is then compared to the pulsed-ring Stark deceleration mode and cases where one mode is superior to another are discussed.
Samples of cold and ultracold polar molecules have the potential to revolutionize physical chemistry, precision measurement, and few-body quantum physics. This thesis describes experimental results for the production of cold samples of OH radicals by Stark deceleration of a supersonic beam. Since Stark deceleration cannot increase the phase space density of the sample, the initial production stage of the OH molecule is critical. The first set of experiments describes a general methodology for the production of OH beams with maximal phase space density, as well as the subsequent coupling to a Stark decelerator. Additionally, we describe the redesign of our electrostatic trap, optimized for future collision experiments of OH with co-trapped ultracold Rb atoms. The new design resulted in a 15-fold increase in total number of trapped molecules over the previous design when tested with ND3 molecules. The second set of experiments focuses on laser-based detection of OH molecules at the exit of the decelerator based on laser induced fluorescence (LIF) and resonance enhanced multiphoton ionizaton (REMPI). The latter method uses vacuum-ultraviolet light at 118nm produced by third-harmonic generation in Xe/Ar gas mixtures as the ionizing step. The sensitivity of this latter technique is limited by the attainable photon flux of the ionizing radiation at 118nm. We present detailed measurements of the conversion efficiencies as well as absolute photon fluxes. Strategies to overcome these limitations as well as prospects for detection of OH molecules in a trap are discussed.
A pinhole discharge unit as well as a dielectric barrier discharge (DBD) head were developed for the Nijmegen pulsed valve (NPV) and the molecular beam properties accessible from each source were characterised and compared. The discharge conditions were optimised for maximum hydroxyl radical density. It was found that the DBD source yields colder OH radicals, whereas the pinhole discharge source provides a threefold larger radical density compared to the DBD discharge head. \n \nTranslationally cold packages of hydroxyl radicals (Ttrans > 1mK) were produced by means of Stark deceleration and a 124-stage Stark decelerator was set up in the laboratory. The decelerator was conditioned, characterised and optimised for operation at low final velocities (v < 40 m/s). The performance of the decelerator was assessed by determining the density of OH radicals available after the deceleration process. \n \nIn a final step, a translationally cold OH package was loaded into a cryogenic magnetic trap. The trap design, the coupling of the magnetic trap to the Stark decelerator and the loading efficiency were numerically optimised employing a direct search algorithm on Monte-Carlo trajectory simulations. The cryogenic environment efficiently prevents black-body radiation from pumping OH radicals out of trappable states and the background pressure improved significantly. Under cryogenic conditions the 1/e trap lifetime improved by a factor of 30 compared to room temperature. The magnetic trap forms part of a hybrid trapping scheme for neutral molecules and ionic species. This novel type of trap represents a versatile environment for investigating ion-neutral molecule reactions in the cold regime, while offering full control over the contributing quantum states.
Currently the fields studying or using molecules with low kinetic energies are experiencing an unprecedented growth.Astronomers and chemists are interested in chemical reactions taking place at temperatures below or around 20 K, spectroscopists could make very precise measurements on slow molecules and molecular physicists could chart the potential energy surfaces more accurately.And the list continues.All of these experiments need slow molecules, with kinetic energies from around 10 cm -1 down to 0. Several designs of cold sources have already been made.The most interesting ones are presented.This work describes the design and the testing of a cold source based on the collisional cooling technique: the molecules of interest are cooled well below their freezing point by a precooled buffer gas.This way condensation is avoided.The source is a copper cell cooled to 4.2 K by an external liquid helium bath.The cell is filled with cold buffer gas (helium).The molecules of choice (ammonia) are injected through a narrow tube in the middle of the cell.The cold molecules leave the cell through a 1 millimeter hole.Two versions of pulsing techniques have been employed: a shutter blade which covers the source hole and opens it only for short moments, and a chopper that modulates the beam further downstream.Both produced pulse lengths around 1 millisecond.The source is tested in an experiment in which the emerging molecules are focused and detected.Time of flight technique is used to measure the kinetic energies.Two detectors have been employed: a microwave cavity to analyze the state of the molecules in the beam, and a mass spectrometer to measure the number density of the particles.The molecules coming out of the source hole are formed into a beam by an electrostatic quadrupole state selector.The quantum mechanical aspects and the elements of electrodynamics involved in the focusing are described.A computer simulation program is presented, which helped calculate the trajectories of the molecules from source to the final detector.The simulations revealed interesting artifacts the focuser can make: if a short state selector is used, the speed distribution of the beam arriving at the detector is strongly modulated by a "focuser transfer function".The essence of the phenomenon is caused by the inability of the focuser to focus all speed at the same time: a few velocity groups are well focused, while many others are defocused.The transfer functions gained from the simulations were used to correctly interpret the detector signal.iii The design of the microwave cavity (Fabry-Perot) and its driving electronics is presented.Due to unavoidable noises present in the circuit, the use of this detector was limited to the preliminary experiments.A simple, commercial mass spectrometer was used.To improve its characteristics, a few modifications have been made.With the improved version, only the water background (an interfering signal at mass 17 amu) was disturbing the signal.A liquid nitrogen trap has been used to minimize the background.The experimental measurements revealed several undesired effects accompanying the production of the slow beam: cluster formation, snow accumulation inside the cell and very high sensitivity to the balance of the two gas pressures.Clusters made up the majority of the emitted particles.Switching from the shutter-blade pulsing (closed cell) to the chopper modulation (open cell) improved the ratio of the useful molecules in the beam significantly.The snow accumulation limited the useful experimenting time to around 20 minutes.After this the accumulated ammonia snow either perturbed the signal significantly or obstructed the source hole completely.A very high sensitivity to the ratio of the buffer gas pressure to the ammonia injection rate has been noticed.A 30% deviation from the optimum value can change the speed distribution and the amount of emitted molecules completely.The stabilization of the ballast pressures was necessary.The beam obtained in the optimal regime of the source cell is presented and analyzed.The characteristic values of most interest in a future collision experiment are the following: the speed distribution of the beam at the detector has a height of the order of 10 5 molecules per unit speed interval and per pulse; the useful speed interval is from 55 m/s to 500 m/s.iv Dedicated to my wife, Magdi.v ACKNOWLEDGMENTS According to an East European folktale a king wanted to find out how much his daughters loved him.When the smallest princess answered "I love you like salt", the angry king banished her from the kingdom.It was only later, when the kingdom was totally deprived of salt, that he realized the real value of his daughter's words.I believe it was the salt of science that I received from my advisor, Frank De Lucia.His endless optimism always kept me going forward and taught me how to deal with difficulties now and in the future.He always made himself available, and never let me go without an excellent idea or a piece of advice.An exceptional scientist and a wonderful man, he will always be the distant example to follow in my scientific career.Gregory Lafyatis also deserves my gratitude for his insights into many of the theoretical aspects of my research.The instruments he lent me made my work in the lab much easier.I also thank Joe Demers for helping me in the lab at the most difficult time: the beginning.I am very thankful to my colleagues, Ivan Medvedev and David Graff for being always interested in my work and giving me valuable ideas.I am especially grateful to Christopher Neese for helping me with LabView related problems at a crucial moment of my research.I wish to thank Kent Ludwig for his tedious work on the low-temperature components of the experimental setup.Tom Kelch, advisor in the student mechanical shop, always had the right solution to the mechanical engineering problems I encountered.The team led by John Spaulding in the main mechanical shop did an excellent work, delivering countless pieces of exceptional quality in a
High-power tunable VUV light pulses with energies up to 0.7 μJ were generated in the 115.7–116.9-nm region by use of a two-photon resonant four-wave mixing scheme in a Xe–Ar gas mixture. This is the highest reported pulse energy that has been produced in this wavelength region using a four-wave mixing process. Efficient detection of krypton isotopes at densities as low as 10 atoms/cm3 was demonstrated by resonantly ionizing the atom through its one-photon allowed state at the vacuum wavelength of 116.49 nm.